1. Field of the Invention
The present invention relates to a temporary adhesive composition which enables bonding between substrates, bonding between a substrate and a support, and the detachment of items that have been bonded together to be controlled by heating the composition. The invention also relates to a method of producing a thin wafer that uses the adhesive.
2. Description of the Prior Art
Three-dimensional semiconductor mounting has become an essential process for achieving increased packing densities and higher capacities. The three-dimensional mounting technique is a semiconductor fabrication technique in which single semiconductor chips are reduced in thickness to form thin chips, and a plurality of layers of these chips are then stacked together, with through-silicon vias (TSV) used for electrical connections between the layers. In order to realize this type of structure, a substrate having a semiconductor circuit formed thereon must be subjected to grinding of the non-circuit-formed surface (also referred to as the “back surface”) to reduce the thickness of the substrate, and electrodes including TSVs must then be formed on the back surface. During the back surface grinding of the silicon substrate, a circuit-formed surface protective tape is bonded to the opposite side of the substrate to the grinding surface, thereby preventing wafer breakage during grinding. However, this tape uses an organic resin film as the base material which, although exhibiting good flexibility, suffers from inadequate strength and heat resistance, meaning it is not suited to the subsequent back surface wiring layer formation process.
Accordingly, a system has been proposed in which the semiconductor substrate is bonded to a support of silicon or glass or the like using an adhesive, thereby achieving a structure that is able to satisfactorily withstand both the back surface grinding and the back surface electrode formation steps. In this system, the adhesive used when bonding the substrate to the support is an important factor. The adhesive must be capable of bonding the substrate to the support with no voids therebetween, have sufficient durability to withstand the subsequent processing steps, and then finally, must allow the thin wafer to be easily detached from the support. Because this detachment is performed in the final step, in this description, the adhesive is termed a “temporary adhesive”.
Conventional temporary adhesives and detachment methods that have been proposed include a technique in which an adhesive containing a light-absorbing substance is irradiated with high-intensity light, thereby decomposing the adhesive layer and enabling the adhesive layer to be detached from the support (Patent Document 1: JP 2004-64040 A), and a technique in which a heat-meltable hydrocarbon-based compound is used as the adhesive, and bonding and detachment are both performed with the adhesive in a heated and melted state (Patent Document 2: JP 2006-328104 A). The former technique requires expensive equipment such as a laser or the like, and also suffers from the problem that the processing time per substrate is long. Although the latter technique is controlled solely be heating, and is therefore relatively simple, the thermal stability of the hydrocarbon-based compound at high temperatures exceeding 200° C. is inadequate, meaning the applicable temperature range is narrow.
Further, a technique that uses a silicone pressure-sensitive adhesive as the temporary adhesive has also been proposed (Patent Document 3: U.S. Pat. No. 7,541,264). In this technique, the substrate is bonded to a support using an addition reaction-curable silicone pressure-sensitive adhesive, and then at the time of detachment, the structure is immersed in a chemical agent that dissolves or decomposes the silicone resin, enabling the substrate to be detached from the support. However, this detachment requires an extremely long period of time, making it difficult to apply the technique to an actual production process.